Fleischer had the idea of using frames of a live action film as the basis for drawing animation, his patent for the rotoscope was granted in 1917, although Max and Dave Fleischer made their first cartoon using the device in 1915.
Fleischer invented the rotograph, the first technique for adding animated characters to live backgrounds. Extensive use of this technique was made in Fleischer's Out of the Inkwell series, one of the highlights being a boxing match between the cartoon Koko the Clown and a live kitten.
Fleischer was also responsible for the "follow the bouncing ball" sing along cartoons.
Fleischer produced the first sound animated cartoons in 1924 using the Lee DeForest sound-on-film synchronization process (years before Steamboat Willie, which the Disney Corporation likes to imply was the first sound cartoon).
Fleischer died in Woodland Hills, California